This invention relates to telephone maintenance termination units having a line protector, and more particularly to a method and associated redundant protector actuation circuitry for use with a telephone maintenance termination unit, to provide convenient and rapid re-establishment of telephone communications.
A telephone system may be viewed as comprising the following three distinct parts:
(a) the telephone company system comprising at least one pair of wires for connecting with a subscriber system,
(b) the subscriber system comprising at least one pair of wires connected to the subscriber telephone and
(c) an interface between the company system and the subscriber system for connecting the telephone company wires to the subscriber wires, known as a maintenance termination unit.
With the advent of the breakup of the single telephone company individual subscribers are permitted to connect their own independently purchased telephones to the incoming telephone lines. The term xe2x80x9clinexe2x80x9d is used to designate a pair of electrically conductive wires.
In order to minimize tampering, and to permit easy connectivity between the subscriber system and the telephone company lines there have been developed maintenance termination units, such as the one described in U.S. Pat. No. 4,979,209. U.S. Pat. No. 4,979,209 (hereinafter the Collins et al. patent) is incorporated herein by reference as it provides a good description of a typical such interface commonly used in the trade. As described in the Collins et al. patent a typical maintenance termination unit includes an individual subscriber line module which includes a generally rectangular, box-like structure including a top, bottom, opposed sides and opposed first and second ends. An individual subscriber line maintenance termination unit is usually provided with a security cover mounted pivotally on one end of the top of the box-like structure which can be locked to limit access to the interior of the box.
In the box-like structure internal space there is at least one individual subscriber circuit comprising at least one pair of subscriber line wiring terminals for connection to the subscriber line, a plug connected to the pair of subscriber wiring terminals, and second electrical connectors for connecting the plug to the incoming telephone company line. The plug is plugged in a socket to interconnect the pair of subscriber wiring terminals and thereby the subscriber line to the incoming telephone company line. Thus the plug provides a demarcation point between the subscriber line and incoming telephone company line. By unplugging the plug from the socket of an operating telephone system one may quickly determine whether a fault exists on the subscriber line or the incoming telephone company line.
In order to provide protection to the telephone system and the subscriber equipment against unwanted and unexpected surge voltages, there have also been developed surge protectors for use with telephone lines. U.S. Pat. Nos. 4,624,514, and 4,447,848 describe such surge protectors
Thus, for each line within the maintenance termination unit there is further included within the box-like structure a removable surge protector. Typically the surge protector is placed between the plug and the incoming telephone line. Surge protectors serve to divert a high voltage appearing in the incoming line from traveling to the subscriber equipment. Typically this is done by diverting the high voltage to ground through some switching system that connects the line to ground when a higher than desired voltage appears on the line. Thus, if a surge protector has been activated there is usually a short to ground in the line between the telephone company and the subscriber. However, the location of such short in the line is not easy to determine from a remote location, because the short may not be the result of an activated surge protector and may be in the subscriber side of the line, the telephone company side of the line or in the activated surge protector.
Because of the presence of potentially dangerous voltages in the maintenance termination unit and the concern about unauthorized tampering with the telephone lines, access to the interior of the maintenance termination unit is preferably limited to authorized telephone company technicians. This in turn requires that a technician be dispatched to physically inspect the maintenance termination units and, if the problem is indeed the protector, replace it to restore the telephone service. This may not be convenient, as telephone interruption may occur at a time where a technician may not be available on short notice. On the other hand if the protector has not been activated dispatching the technician to inspect it is a waste of time and resources.
There is, therefore still need for a simple, safe and secure way for the telephone company to ascertain whether the suspected activated protector is indeed the problem and be able to restore service preferably without having to immediately dispatch a technician to the subscriber""s location.
According to this invention there is provided a device for use in a maintenance termination unit, the device comprising:
(a) a pair of input line connectors for connecting to a first telephone line
(b) a pair of output line connectors for connecting to a second telephone line;
(c) at least one pair of first protector connectors for connecting to a first protector circuit;
(d) at least a pair of second protector connectors for connecting to a second protector circuit; and
(e) a switch for selectably routing an electrical signal appearing at said input line connectors to said at least one pair of output connectors through a selected one of said first and second protector circuits.
The device may be housed in a casing designed as a replaceable plug adapted to fit within a socket in a typical maintenance termination unit. There is thus also provided according to the present invention, a maintenance termination unit comprising:
(a) at least one input line connector;
(b) at least one output line connector;
(c) at least two independent surge protectors; and
(d) a switch connected to said at least one input line, said at least one output lines and said at least two independent surge protectors for selectably routing an electrical signal appearing at said at least one input line connector to said at least one output line connector through a selected one of said at least two independent surge protectors.
The switch may be an electronic switch and switching may be accomplished using a detector circuit to detect a surge voltage activation of the protector circuit and a control circuit to generate a signal indicative of the protector activation. The signal may be used to provide a visual indication or may be used to automatically disengage the first protector from the line and engage the second protector restoring service.
Finally there is also provided according to this invention a method for replacing a first protector circuit connected between an input and an output line pair in a maintenance termination unit, the method comprising:
(a) providing a second protector circuit;
(b) connecting a first switch between said input line pair and said first and second protector circuits;
(c) connecting a second switch between said first and second protector circuits and said output line pair; and
(d) switching both switches and connecting one of said first and second protector circuits between said input and said output line pairs.